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Recent content by charz

  1. charz

    Gas group IIA vs IIB, IIC

    Does that mean IIA, IIB & IIC motors of same rating would have the same frame size? and there would no be issue during replacement? Which gas group is available immediately in the market so that delivery times are lesser?
  2. charz

    Arc Resistant Switchgear

    When to buy an arc resistant switchgear? If I buy an arc resistance switchgear, Can I open the controls compartment of HV or LV switchgear without PPE? Am I safe when I open the door/panel of one de-energized compartment? While the adjacent compartment remains energized. Do I still need to wear...
  3. charz

    Gas group IIA vs IIB, IIC

    How common (as a standard product) is the availability of gas group Ex de IIA, Ex ec IIA motors? As I could see from our past projects, most LV motors are with gas group IIB, so IIB looks more common. The concern here is that vendor is offering gas group IIC for some motors; if I accept the IIC...
  4. charz

    Isochronous load sharing lines for generators in parallel (Island system)

    Depending on the amount of load to be added/removed (variations)? If the variations are low: one in ISO and other machines in droop are preferable, since the ISO machine can handle variations in load without getting overloaded or motored. If the variations are high: All machines in droop are...
  5. charz

    Distribution board or main switchboard

    I have a sub main distribution board which feeds the final distribution boards and 10's of individual loads. Now considering that I have an option of applying both MCBs and MCCBs as the outgoing circuit breakers. MCBs - Standard ratings are available from 0.5A to 80A. MCCBs - Standard ratings...
  6. charz

    Distribution board or main switchboard

    Can MCCB and MCB be put in the same sub distribution panel?
  7. charz

    SCCR rating

    Dialed the manufacturer, he says the peak value is 225kA and waiting to receive the test report.
  8. charz

    SCCR rating

    My specification calls for a short circuit rating of 35kA rms and 77kA peak value for a junction box with a bus bar in it. The vendor proposes a junction box with a short circuit tested at 90kA for 0.1s. He justifies that peak mechanical effects (potential damage) to a product due to a short...
  9. charz

    Purpose of 87N Circuit

    Because fault currents are very less as the faults get closer to neutral, this can be detected by REF whereas Differential may not detect this. As most of the times, the faults of those lesser magnitude comes under the slope setting.
  10. charz

    Dual UPS - Autonomy Timer setting

    Hi Mike, One line is attached.https://files.engineering.com/getfile.aspx?folder=9f682237-72b6-4d69-be4a-c9038d7bcb5b&file=Dual_UPS_SLD.pdf
  11. charz

    Hazardous Area Certification - Saudi Aramco

    The Saudi Aramco specification says, 8.3.1 IEC or Ex labeled equipment/component meeting requirement of IEC 60079 and certified by one of the agencies in the approved IECEx certification bodies (ExCBs) under IECEx Certified Equipment Scheme is acceptable. Method of protection must be marked...
  12. charz

    Exciting Current of CTs - Differential / REF

    The attached article says that the relay setting should be above the sum of the exciting currents in the parallel CTs. ( I got this article from one of the old threads on this same forum). Does it mean the exciting currents of the CTs circulates through the relay path? how does the exciting...
  13. charz

    CT Polarity - In differential protection

    If understand that "P2" (Primary) of the CTs to be positioned towards the protected object; My question is concerned with the other core in the CT supplying to Metering in the secondary of the power transformer - green highlighted in the below image, Is there a possibility to wrong polarity...
  14. charz

    CT Polarity - In differential protection

    Yes, it is not connected to the Diff/REF relay in the above picture. That is why I asked you to consider. These pictures are not related to my project. If these CTs are connected to the Diff/REF relays, is the position/polarity of the CTs are correct. As I studied, these position of CTs are...
  15. charz

    CT Polarity - In differential protection

    Dear Mr che, My question is related to the position of the primary of CTs for differential and REF protections. Generally P1 of the CT is connected to the source side and P2 is connected to the load side. In the above image, consider the top portion as primary of the power transformer (source...
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